The present invention relates to a large scale integrated circuit, and more particularly to a high-density integrated semiconductor device constituted by a voltage converter circuit and miniaturized devices (devices with small dimension) which can keep up with a wide range of an operating power-supply voltage and kinds of power supplies, i.e. a large scale integrated circuit in which integrated on a monolithic chip are a microcomputer, a logic circuit, a dynamic RAM (random access memory), a static RAM, a ROM (read-only memory), etc.
In recent years, onto the market have come portable electronic machines such as a lap-top type personal computer, an electronic pocket notebook, etc., and portable electronic media machines such as a solid-state voice recorder which performs voice recording without using a magnetic medium, a solid-state camera (electronic still camera) which performs image recording without using the magnetic medium. In order for these portable electronic machines to be widely popularized, it is indispensable to realize an ultra large scale integrated circuit (ULSI) which permits a battery based operation or an information (data) retention operation using a battery (battery back-up). On the other hand, there has been increased demand for a semiconductor disk, which can provide higher speed accessing than a magnetic disk, as a large-capacity-file memory system for implementing a computer with higher performance. And this semiconductor disk requires a very large-capacity memory LSI which can perform the information using a battery.
The ULSIs used for these applications must satisfy the following requirements.
(1) The operation in a wide range of operating power supply voltage (1-5.5 V). This requirement permits one-chip ULSI to be adapted for many kinds of power supplies including, e.g. 5 V which is a standard power supply voltage for the present TTL compatible digital LSI, 3.3 V which is one candidate for the standard power supply voltage for the future TTL reversible digital LSI, 3-3.6 V which is a typical output voltage of a primary cell of lithium, etc., 1.2 V which is a typical output voltage of a secondary cell of cadmium and nickel, and so on.
(2) The measures for a secular change or time-dependent fluctuation (for a short period or long period) in the power supply voltage. This requirement removes fear of operation failure due to voltage fluctuation resulting from the secular change in the cell voltage and the switching of power supply in shifting between the operation under a nominal condition and a battery back-up operation.
(3) The power reduction in the standard operation or the battery back-up operation. This requirement permits a small-sized battery to operate the ULSI for a long period.
(4) The reduction in a switching current. This requirement decreases voltage fluctuation caused by switching in the battery voltage, thus preventing the operation failure.
One example of the product of microprocessor which operates in a wide range of the operating voltage is disclosed in the 4-bit microprocessor handbook, p 148 published by NIPPON DENKI Co., Ltd. The product name is xcexcPD7507SC. The range of the power supply voltage in this microprocessor is 2.2-6.0 V. Information in a data memory (static RAM) is retained with a minimum voltage of 2 V. In this memory, the recommendable voltage is generally 5 V for the operating power supply voltage and for 2 V the data retention.
An example of the dynamic memory for battery back-up in which power consumption in the data retention (refresh) is decreased is disclosed in IEEE, Journal of Solid-State Circuits. Vol. 23, No. 1, pp. 12-18, February 1988. The power supply voltage is 5 V for both nominal operation and data retention.
An example in which an external voltage is dropped to be supplied to an internal circuit is disclosed in U.S. Pat. No. 4,482,985.
An example of the battery back-up for a memory is disclosed in U.S. Pat. No. 4,539,660.
A technique for changing the plate voltage of a dynamic RAM is disclosed in Japanese Patent Publication No. 61-61479.
The battery back-up of a static RAM is disclosed in the catalogue published by Hitachi, Ltd., pp. 44-45.
The other relevant references and patent publications will be identified in the following description.
The present invention intends to lower the operation voltage of a system provided on a monolithic chip so that the operation speed is not affected by changes in the power supply voltage supplied from the outside.
The present invention has been accomplished by devising voltage converter means which is capable of stably supplying a fixed voltage in a wide range of power-supply voltage. The voltage converter means in the present invention is referred to as means including at least one amplifier which generates an output voltage on the basis of an input reference voltage, and is different from means of only dropping voltage using resistors, etc.
In the present invention, it is also critical to improve a dynamic RAM which is the biggest obstacle against lowering the operation voltage. This is because the dynamic RAM requires a refresh operation even during data retention due to its dynamic operation and so does not permit only the operation voltage during data retention to be lowered unlike the static RAM.
The microprocessor and static RAM as mentioned above have a wide range of the operating power-supply voltage of 2-5 V. However, since they are designed around the power supply voltage of 5 V, the operation speed thereof (the highest clock frequency in the case of the microprocessor and access time in the case of the static RAM) is not assured for the operation outside the recommended fluctuation (generally, +10%) in the power supply voltage. Particularly at a low power supply voltage, it is common that the operation speed is greatly lowered. The dependency of the operation speed on the power-supply voltage is different with the products. Therefore, the operation speed of a system must be designed to accord with the lowest one of the operation speeds of LSIs constituting the system. This made it impossible to provide a necessary performance of the system for the operation outside at 5 V and difficult to design the system for the operation at a low power supply voltage.
These LSIs, the lowest operating power supply voltage of which is 2.2 V, are difficult to adapt to all of many power kinds of power supply voltages as mentioned above, which is a restriction to system design. Further, the dynamic RAM to be incorporated in the system, the lowest operating power supply voltage of which is 4.5 V, are further difficult to adapt to the many kinds of power supply voltages. Particularly, the absence of different between the power supply voltage for normal operation and that for data retention made very complicated the arrangement of a power supply switching circuit, thereby making the data retention difficult.
Meanwhile, with rapid development of miniaturization (scaling down) of semiconductor devices, by using the processing technology lower than 0.5 xcexcm, it is possible to constitute a so-called system LSI in which several LSI blocks are integrated on a monolithic chip. In such a system LSI, it is required that the operating power-supply voltage ranges and operating speeds of the respective LSI blocks are aligned with each other. However, as mentioned above, only combining the conventional LSIs could not constitute such a system LSI.
The present invention can be constituted by an LSI circuit block which has a power down mode suited for battery back-up can operate at a low power supply voltage of about 1 V at the minimum; a power supply voltage converter circuit which supplies an internal power supply voltage suitable to the operating mode to the LSI; and an input/output circuit for converting the signal amplitude.
By operating the main LSI block, which performs storage and processing of information, at a substantially fixed low voltage regardless of the external power supply voltage, it is possible to provide substantially constant operation speed performance over a wide range of the power supply voltage. The external power supply voltage can be reduced to the operation voltage of the LSI block as required so that power consumption during data retention can be reduced to a necessary and minimum value and also a battery back-up circuit can be simplified in its constitution. Further, the optimum operation voltage according to the characteristic of miniaturized devices constituting the main LSI block can be set independently of the external power supply voltage so that performances of high integration degree, high operation speed, and low power consumption can be obtained simultaneously.
An object of the present invention is to provide a large scale integrated circuit (LSI) which can operate at a fixed operation speed against wide range fluctuation of an operating power supply voltage.
Another object of the present invention is to provide voltage converter means which can produce a constant output voltage against wide range fluctuation of the operating power supply voltage.
Still another object of the present invention is to reduce power consumption in an LSI and particularly the power consumption during battery based operation.
Yet another object of the present invention is to prevent operation failure of an LSI which performs a low voltage operation.
A further object of the present invention is to provide an LSI with a plurality of input/output levels.
A further object of the present invention is to provide a dynamic RAM which can perform a low voltage operation.
A further object of the present invention is to improve a sense amplifier used for the dynamic RAM which performs a low voltage, and its operation.
These and other objects and many of the attendant advantages of the present invention will be readily appreciated as the same become better understood by reference the following detailed description when considered in connection with the accompanying drawings.